#include <stdio.h>
int parte(int n)
{
    int p=5,s=0;
    while(n/p!=0)
    {
        s+=n/p;
        p*=5;
    }
    return s;
}
int main()
{
    int n;
    FILE *f=fopen("fact.in","r");
    fscanf(f,"%d",&n);
    fclose(f);
    FILE *g=fopen("fact.out","w");
    int st,dr,mij,elem=-1,z;
    if(n==0)
    {
        fprintf(g,"1");
        return 0;
    }
    st=0;
    dr=5*n;
    while(st<=dr) {
        mij=(st+dr)/2;
        z=parte(mij);
        if(z>n)
            dr=mij-1;
        else {
            if(z<n)
                st=mij+1;
            else
            {
                elem=mij;
                dr=mij-1;
            }
        }
    }
    fprintf(g,"%d",elem);
    return 0;
}